Mix Result

What it is

The Mix Result tool answers a forward question: “what do I end up with?” It works two ways, switched by the Fill / Decant toggle at the top. The difference is where the pressure gauge is.

• Fill: you add measured gas to one cylinder from a bank or supply, reading that cylinder’s own gauge. Use it for “add 20 bar of O₂, then 100 bar of air, what do I get?”.
• Decant: you join two cylinders with a transfill whip and read the single gauge on the whip. Use it for “I poured one cylinder into another, what’s in each now?”.

The in-app title is “Mix Result”. It lives at the plan/mix-calculator route.

Fill mode

Set the cylinder’s current contents and pressure, list the gases you’re adding, and the tool gives you the resulting mix and final pressure after each addition.

1. Set the current cylinder: its O₂%, He%, and pressure. Both fields always show, so leave He% at 0 for air or nitrox and set it for trimix or heliox. Or tap Quick Fill to load a saved cylinder profile in one tap.
2. Add one or more gases under Add Gas, each with its O₂%, He%, and the pressure to add. That figure is how far this cylinder’s own gauge climbs, not the final pressure: to top a cylinder from 50 to 150 bar, add 100 bar. The form opens pre-filled to 100% O₂ at a 5 bar increase.
3. Optionally open the collapsible Environment section to set altitude and the fill versus ambient temperature.
4. Read the Steps and the final gas. Reset clears it back to the start.

Decant mode

Decant covers the other scenario: two cylinders joined by a transfill whip. You open both and let them equalize. When the gas stops flowing, both cylinders, and the whip gauge, sit at one settled pressure: the average of the two starting pressures weighted by cylinder size. A whip equalizes pressure but not composition, so only the lower-pressure cylinder’s mix changes (it takes on the other cylinder’s gas), while the higher-pressure one keeps its mix and just drops to the settled pressure. There is no source or target to pick: the tool works out which way gas flows from the two pressures.

1. Enter Cylinder A and Cylinder B: each one’s size (water volume), current pressure, and mix. Quick Fill loads a saved cylinder.
2. Read the result: the settled pressure both reach, and the mix and pressure each cylinder ends at once the gas stops flowing. The cylinder that received gas is marked.

If both cylinders start at the same pressure, no gas flows and the tool says so.

To plan a partial transfer (top a cylinder up toward a target mix, stopping before they fully equalize), use the Gas Blender’s Decant mode instead. That is a planning operation, not something Mix Result estimates.

How Mix Result differs from the Gas Blender

These tools run the same physics in opposite directions.

• Mix Result (this tool) works forwards: you know what you did (a fill or a decant) and it tells you the mix you get.
• Gas Blender works backwards: you give it the mix you want and it tells you the steps to reach it. The Blender has its own Decant mode too: give it a target mix for the cylinder you’re topping off and it tells you the pressure to fill the receiver to, plus what is reachable from your donor.

Reach for Mix Result when you’re starting from what’s in the cylinder. Reach for the Gas Blender when you’re starting from the mix you need.

Inputs and outputs

Input	Meaning	Notes
Current O₂% / He%	What’s already in the cylinder	Both fields always show; set to 0 for nitrox, enter a value for trimix or heliox
Current pressure	Starting cylinder pressure	Gauge pressure, in your unit (bar or psi)
Added gas O₂% / He%	Composition of each gas you add	One row per addition
Added pressure	How much pressure each addition contributes	Sequential, in order
Altitude	Sets atmospheric pressure	Optional; matters for accurate blending
Fill / ambient temperature	The temperature during filling and where the gas settles	Optional; drives the cooldown/warm-up step

Output	Meaning
Starting gas	The cylinder state you began with
Steps	Step-by-step O₂%, He%, and pressure after each addition
Cool down / warm up step	The “Cool down to X” or “Warm up to X” line that appears in Steps when fill and ambient temperatures differ
Final gas	The resulting O₂%, He%, and pressure

How the math works

Mixing uses Dalton’s Law of partial pressures on absolute pressures (gauge plus atmospheric):

FO₂_final = (P_abs_current × FO₂_current + dP × FO₂_added) / P_abs_final

Helium mixes the same way. Oxygen and helium fractions don’t change with temperature, but pressure does, so the temperature correction uses Gay-Lussac’s Law:

P_settled = P_hot × (T_ambient_K / T_fill_K)

That’s why a hot fill shows a “cool down to” step and a cold fill shows a “warm up to” step. All of this runs in Decimal.js for safety-critical precision.

In Decant mode, the settled pressure two joined cylinders reach is the volume-weighted average on absolute pressures:

P_settled = (P_A × V_A + P_B × V_B) / (V_A + V_B)

Both cylinders end at that settled pressure. The lower-pressure cylinder’s new mix is the same partial-pressure blend as a Fill top-up, using the higher cylinder’s gas; the higher cylinder keeps its mix. Decant uses altitude only, no temperature settling, and the settled gauge pressure does not depend on altitude.

Pressure reads in your chosen unit (bar or psi); the calculation is metric internally and converts at the display boundary.

Real gas, not the ideal-gas rule

Fill mode uses a real-gas (compressibility) model, not the ideal gas law that blending courses teach for hand calculation. At fill pressures the gases do not pack quite the way the simple rule assumes, so a result can differ by a fraction of a percent from what a partial-pressure chart predicts. For nitrox the gap is tiny, well inside what your analyzer reads. It is larger and one-directional for helium, where an oxygen analyzer cannot catch the error, so getting the number right up front matters more for trimix. Dive Kit’s number is the one closer to what you will actually analyze. Decant uses the same real-gas model.

Behaviour and limits

The result is a calculation, not a measurement. Always analyse the finished cylinder with an oxygen (and helium) analyser before diving, and label it.

Input ranges: pressure goes up to 330 bar (4787 psi), altitude up to 10000 m, and fill and ambient temperatures from -50 to 100 C. If an addition would push the mix over 100% O₂, the tool rejects it and the result panel simply goes blank with no number shown. That blank panel is your signal that the fill is impossible as entered, not a bug. Lower the added pressure or the added O₂% until a result appears.

Decant uses the real-gas model for both the settled pressure and the resulting mix, but assumes an isothermal transfer. In the real world a freshly decanted cylinder is warm, so once it cools it reads a little lower than the settled figure, and a transfill whip holds a small dead volume of gas. A whip is also too slow for the two mixes to blend across it, which is exactly why the lower cylinder ends up with a different mix from the higher one. Analyse both cylinders after the gas settles.

Related

• Gas Blender is the reverse tool: give it the mix you want and it gives you the fill steps to get there.